Electroacoustic sound reinforcement units with an acoustic horn or waveguide are often used in sound reinforcement systems for use out of doors or in large rooms. These sound reinforcement units are more particularly suitable for reproducing medium and high frequencies. A horn or acoustic waveguide is defined between a throat, to which an electroacoustic transducer (i.e. a loudspeaker or a compression chamber driver) is connected, and a mouth, from which the sound propagates into the exterior medium. The shape of the horn or waveguide can be characterized by a function defining the expansion of its cross section between the throat and the mouth, i.e. the variation of said cross section along a defined propagation axis between said throat and said mouth. The function can be linear, exponential or otherwise. It is generally an increasing function between the throat and the mouth. The three parameters previously cited, namely the area of the throat, that of the mouth, and the expansion function, determine the dispersion of the acoustic wave at the exit of the horn or waveguide. As a general rule, dispersion increases with expansion. At low frequencies, dispersion control improves as the area of the mouth increases and at high frequencies dispersion control improves as the area of the throat decreases.
The optimum dispersion characteristics vary with the configuration of the sound reinforcement site. An important part of the know-how of sound engineers therefore consists in choosing sound reinforcement units with the most suitable dispersion characteristics. They must therefore have available a large number of sound reinforcement units with entirely different characteristics, in particular different horn or acoustic waveguide shapes and dimensions. The invention overcomes this drawback. The basic idea of the invention is that the same sound reinforcement unit can have its dispersion characteristics adapted by modifying one or more of the parameters defined hereinabove and in particular the expansion function of the horn or waveguide.